Polyether urethanes containing reactive silane groups, also referred to as silane-terminated polyurethanes (STPs), and their use as sealants and adhesives is known and described, e.g., in U.S. Pat. Nos. 5,554,709; 4,857,623; 5,227,434 and 6,197,912; and WO 02/06367. The silane-terminated polyurethanes may be prepared by various methods. In one method the silane-terminated polyurethanes are prepared by reacting diisocyanates with polyether polyols to form isocyanate-terminated prepolymers, which are then reacted with aminosilanes to form the silane-terminated polyurethanes. The sealants may also be prepared by reacting unsaturated monools with diisocyanates to form intermediates containing unsaturated end groups and then converting these unsaturated groups to alkoxysilane groups by hydrosilylation. In another method the sealants are prepared in one step by the reaction of polyether diols with isocyanatosilanes
To be useful as sealants the silane-terminated polyurethanes should have a number average molecular weight of 6000 to 20,000. One method of obtaining this molecular weight is to use polyether diols prepared by the KOH process and having a molecular weight of 2000 to prepare the isocyanate-terminated prepolymers. The presence of urethane groups causes the products to have a high viscosity. To achieve suitable application viscosities, the high viscosity is reduced by the addition of higher amounts of plasticizer and lesser amounts of fillers, resulting in more expensive sealant products.
Another method of obtaining high molecular weight sealants is by using high molecular weight polyether diols having a low degree of unsaturation and prepared using special catalysts as described in EP-A 0,546,310, EP-A 0,372,561 and DE-A 19,908,562. When these polyether diols are used, the resulting sealants have excellent tensile strength, but the sealants are too brittle for many applications because the elongation is too low and the 100% modulus is too high.
It is an object of the present invention to provide polyether urethanes that have reactive silane groups and are suitable for use as sealants, adhesives and coatings which possess high tensile strengths and elongations and have a reduced 100% modulus when compared with existing products.
This object may be achieved with the polyether urethanes containing reactive silane groups according to the present invention. These polyether urethanes contain a mixture of polyether urethanes containing two or more reactive silane groups with polyether urethanes containing one reactive silane group. The polyether urethanes containing two or more reactive silane groups are prepared from high molecular weight polyether polyols having a low degree of unsaturation and the reactive silane groups are incorporated by the use of primary aminosilanes. In the polyether urethanes containing one reactive silane group, the reactive silane groups are incorporated by the use of secondary amino-functional silanes.
The silane-terminated polyether urethanes according to the invention are suitable for the preparation of sealants or adhesives that have higher tensile strengths and elongations and lower 100% moduli. Due to the fact that these polyether urethanes have a low viscosity, sealant compositions can be formulated with less of the more expensive plasticizers and more of the less expensive fillers, resulting in less expensive sealants.
The preparation of sealants from mixtures of polyfunctional and monofunctional silane-terminated polyurethanes is known and disclosed in U.S. Pat. Nos. 5,554,709 and 4,857,623 and WO 02/06367. However, these references do not disclose the use of polyether polyols having a low degree of unsaturation and aspartate-functional silanes to prepare the sealants.
The preparation of silane-terminated polyether urethanes from aspartate-functional silanes is disclosed in U.S. Pat. No. 5,364,955 and WO 98/18843. In both of these references the polyethers used to prepare polyether urethanes do not have a low degree of unsaturation. In addition, mixtures of polyfunctional and monofunctional silane-terminated polyurethanes are not disclosed. Finally, in the latter reference the polyethers must contain 15 to 40% by weight of ethylene oxide units.
WO 00/26271 discloses the preparation of silane-terminated polyether urethanes from polyether polyols having a low degree of unsaturation and aspartate-functional silanes. The products are prepared by reacting diisocyanates with high molecular weight polyether diols to form NCO prepolymers, which are then capped with aspartate-functional silanes to form silane-terminated polyether urethanes. This application does not disclose mixtures of disilane-terminated polyether urethanes with polyether urethanes containing one reactive silane group.
U.S. Pat. No. 6,265,517 describes a similar process for preparing silane-terminated polyether urethanes from polyether polyols having a low degree of unsaturation and aspartate-functional silanes. The patent requires the starting polyol to have a monool content of less than 31 mole %, and teaches that a relatively high monool content is highly undesirable because monools react with isocyanates thereby reducing crosslinking and curing of the prepolymer. The patent also requires the aspartate silanes to be prepared from dialkyl maleates in which the alkyl groups each contain more than four carbon atoms.
EP 0,372,561 discloses polyether urethanes containing reactive silane groups and prepared from polyether polyols having a low degree of unsaturation. In addition, polyether urethanes containing one reactive silane group are disclosed. This application fails to recognize the necessity of using secondary amino-functional silanes to incorporate reactive silane groups into the polyether urethane containing one reactive silane group.
Copending applications, Ser. Nos. 10/160,463, 10/174,039, 10/160,479 and 10/160,364, disclose alkoxysilane-functional polyether urethanes containing a mixture of polyether urethanes containing two or more reactive silane groups with polyether urethanes containing one reactive silane group. The polyether urethanes containing two or more reactive silane groups are prepared from high molecular weight polyether polyols having a low degree of unsaturation.